Grinding machine



Aug. 3, 1943. H. B. BARRETT 2,325,826

GRINDING MACHINE Filed Apfil 3, 1941 5 Sheets-Sheet l HARRY B. BARRETTlA-vf(- ATTORNEY Aug. 3, 1943. H. B. BARRETT GRINDING MACHINE 5'sheets-sheet 2 Filed April 5, 1941 HARRY B. BARRETT ATTORNEY Aug- 3,1943. H. B. BARRETT 21,325,826

GRINDING MACHINE Filed April 5, 1941 5 Sheets-Sheet 3 INVENTOR. HARRYB'. BARRETT @www ATTORNEY Aug. 3, 1943. H. B. BARRETT GRINDING MACHINEFiled April 5, 1941 5 Sheets-Sheet 4 mfENTQR. HAR RY B BARRETT Lid-LALAgni-f,

AT TC- Pl N E Y All@ 3, 1943 H. B* BARRETT 2,325,826

GRINDING MACHINE Filed April 3, 1941 5 sheen-sheet 5 O INVENTOR. HARRY BBARRETT Fusie. C

` ATTORNEY Patented Aug. 3, 1943 GRINDING MACHINE Harry B. Barrett, St.Louis, Mo.

Application April 3, 1941, Serial No. 386,668

12 Claims.

This invention relates generallyl to abrading or grinding machines orapparatus and, more particularly, to certain new and useful improvementsin abrading or grinding machines especially adapted for grinding arcuatesurfaces, such, for instance, as applied automotive brake linings andthe like.

My invention has for its primary object the provision of a grindingmachine which is uniquely capable of producing to a selected orpredetermined diameter a precise, accurate, smooth, and even surfaceupon the wearing face of a. lined brake-shoe either when the brake-shoeis separate ordetached from the brake-assembly or when the brake-shoe isfully assembled in its operating position, so as to obtain substantiallyperfect braking engagement between the brakeshoe and its companion drum.y

My invention has for a further object theprovision of a machine of thetype and for the purposes stated which is simply and convenientlymanipulable for the performance of accurate work even in the hands ofrelatively unskilled mechanics, which is rugged, durable, and economicalin construction, which is extremely adaptable to a Wide range ofdiametral sizes and is hence substantially universal in character,which, in association with a few simple readily applied accessories, isreadily capable of performing all of the essential grinding operationsrequired in the relining of automotive brakes, and which is highlyelhcient in the performance of its stated functions.

And with the above and other objects in view, my invention resides inthe novel features of form, construction, arrangement, and combinationof parts presently described and pointed out in the claims.

In the accompanying drawings (ve sheets)- Figure 1 is a top plan view ofan abrading or grinding machine constructed in accordance with andembodying my present invention;

Figure 2 is a sideelevational view of the machine;

Figure 3 is an enlarged longitudinal sectional view of the machine;

Figures 4, 5, and 6 are detail ltransverse sectional views of themachine taken along the lines 4 4, 5 5, and 6 6, respectively, Figure3';

Figure 7 is a fragmentary top plan view of the machine, illustrating indetail several selected positions of the swingable carriage-plate;

Figure 8 is a fragmentary top plan view of the machine, illustrating theoperation of the accessory or associated calipers;

Figure 9 is a vertical sectional view of themachine taken approximatelyalong the line 9 9, Figure 8;

Figures 10 and 11 illustrate in front and side elevation, respectively,a jig-frame tted with suitable accessory or associated elements in theprovision of a portable concentric abrading tool adapted for grindingcertain types of brake-shoes in situ;

Figures 12 and 13 are transverse sectional views taken approximatelyalong the lines I2-I2 and I3 I 3, respectively, Figure 10;

Figure 14 illustrates in-top plan View a combination tool comprising anadapter plate for accommodating the carriage plate and jig-frame of thepresent machine;

Figure 15 is a fragmentary side elevational View of the combinationtoolor machine of Figure 14; and

Figure 16 is a detail vertical sectional view taken approximately alongthe line Iii-I6, Figure 15.

Referring noW in more detail and by reference characters to thedrawings, which illustrate a preferred embodiment of my invention, theprimary grinding machine, generally designated A, comprises a preferablycast-ironv base-plate I having a depending marginal flange 2, the plateI being of T-shape in horizontal contour and upon the rear base-portion4, is a conventional preferably high-speed electric motor 8 controlledby a manually actuable switch 9 and connected by suitable conduit means(not shown) to any conventional source of electric current, the motorshaft I 0 projecting forwardly through a registering aperture II in ashallow cast-iron wheel guard I2, in turn, upstanding from, and rigidlybolted or otherwise suitably secured to and along the rear transversemargin of, the forward base-portion 3, as best seen in Figure 2. Keyedupon the shaft I0 for rotation within the connes of the guard I2, is agrinder Wheel I3 renewably provided upon its front face with a vsuitableabrasive surface or disk. and upon its rear face with preferablyintegral radially curved impeller flanges I5, a supplemental or frontguard closure I6 having a Asuitably flanged openingII for permittingconvenient access to the abrasive surface or disk I4 being removably ordetachably fastened upon the guard I2, as shown.

Registrably beneath the wheel-guard I2, the base I isprovided-transversely with a somewhat semi-circular depression or troughI8 which opens upon a side face of the base I in the provision of atubular discharge pipe I9 for connection to a suitable catch-bag orother dust disposal means (not shown).

Attached as by means of a removable pivotscrew for swingable movement toand upon the base-portion 3, is an",` L-shaped carriage 2I, whichincludes a forwardlyvor longitudinally projecting leg 22 and atransversely extending leg 23. On its under face, the lateral leg 23A isaccurately machined to be truly perpendicular to the axis of thepivot-screw 20 for riding smoothly over the machined upper face 3 of thebase I and along its rear margin is provided with a rearwardlyprojecting ear24 having an arcuate slot 25 substantially concentric withthe axis of the pivot-screw 2l) for accommodating a clamping bolt 26threaded into the base I. vOn its lateral face, the ear 24 is'providedwith a reference line or graduation 21 for coincidence with anindex-mark 28 suitably inscribed upon the base I, as best shown inFigure 7.

The forwardly or longitudinally extending carriage leg 22 is machinedupon its upper face in the provision of a reference surface 29accurately parallel to the plane of the machined basesurface 3 and isformed with a plurality of vertically disposed openings 30, the centersof which are accurately located at predetermined distances forwardlyfrom the grinding plane or face of the grinder wheel I3 and are eachsuitably marked with appropriate designating numerals. As shown, in thepresent instance, the openings or apertures 30 are located respectivelyat distances of ve, five and one-half, six, six and one-half,

seven, seven and one-half, and eight inches from such grinding surfaceand are, accordingly, desaszasae ciated reference mark 28 are in precisealignment.

Suitably fixed in the plate 3I in laterally spaced u relation to theaperture 32 and projecting for- 14, 15, and .16 to indicate respectivebrake shoe diameters, for the accommodation of which the present machinemay be accordingly adjusted, as will presently be fully described.

Bolted or otherwise suitably secured to and upon the forward margin of,and projecting ver'- tically downwardly from, the carriage-leg 22, is aflange or plate 3l apertured, as at 32, for loosely embracing the shankof a horizontally disposed carriage-adjustment screw 33 threaded at itsrear end in a suitably drilled and tapped boss 34 registrably locatedinthe forward transverse portion of the base-flange 2.

' At its forward end, the screw 33 is provided with a knurled knob 35having a cylindrical skirt 36, suitably inscribed u'pon the peripheralface of which is an annular series of circumferentially spacedgraduations forming a scale extending from "0 to 99.

Rotatably mounted upon the screw 33 intermediate the knob 35 and thedepending plate 3|, is an indexing thrust collar 31 machined upon itsforward face for smooth'rotatable engagement with the rearwardlypresented face of the knobskirt 36 and provided upon its rar face with arearwardly projecting arcuate engagement'boss 38 for abutment againstthe forwardly presented face of the plate'3l. Fixed in, and extendinghorizontally from the rear face of, the collar 31, is a pair of spacedparallel pins 38' sized for snug-fitting slidable engagement with theupper and lower faces oir the aperture 32 for holding the collar 31against rotation when the screw 33 is turned, the collar 31, upon itsperipheral face, being provided with a single reference mark 39 wardlybeyond the knob 35, is a horizontally disposed carriage-shifting rod 40provided at its outer end with a suitably shaped handle or knob 4I,

Coiled loosely about the screw 33 and impinging at its opposite endsagainst the base flange 2 and -the plate 3II is a compression spring 42for yieldingly retaining the plate 3I and the associated carriage 2Inormally in outwardly disposed abutment against the boss 38 of thethrust collar .31, all as best seen in Figures 2, 3, and '1 and forpurposes presently fully appearing.

Adapted and designed for threaded disposition at its one or lower end inany selected one of the carriage-apertures 30 to upstand from, andsubstantially at a right-angle to, the carriage 2 I, is a suitablepintle 43 formed rintermediate its ends with a diametrally reducedbearing-section 44 and a thrust-shoulder 45. Adjacent its (upper end,the pintle 43 is provided with a knurled section 46 having a diametralbore 41 for removably f accommodating a suitable tightening rod or othertool, not shown, the pintle 43, at its upper end, having a diametrallyreduced cylindrical portion 48 registering with the bearing portion 44.

49 designates a jig-frame which includes a body-member preferably in theform of va. rectangular casting 50 having accurately machined parallelupper and lower faces 5I, 52, respectively, and a centrally disposedbearing 53, the axis of which is perpendicular to the plane of suchmachined faces 5I, 52, for accurate engagement around .the bearingportion 44 of the pintle 43 for detachably securing the member 49 'forswingable movement horizontally over the carriage 2I,

a free-rotating thrust washer .54 being preferably disposed between theupper face of the casting 50 and the thrust collar 45 of the pintle 43.

Extending for lengthwise movement through the casting 50 and forming apart of the jigframe 49, is a pair of spaced slide rods -preferablyparallel with the' machined casting faces and rigidly cross-connected atone end by a transverse casting 56 having'an upstanding preferablyintegral index-finger 51 provided upon its upper face with a suitableindex-line 58.

At their opposite end, the rods 55 are rigidly cross-connected by ahead-block 59 having a centrally disposed tapped drill hole 60 andprovided with accurately machined upper and lower faces 6I,- 62,respectively, having a laterally projecting f tongue 63 and a transversemilled slot 64, the tongue 63 and slot 64 both being preferably disposedaccurately at right angles to the longitudinal axis of the frame 49.

The jig-frame 49 further includes a leada screw 65, which isdisposedfpreferably midway between and parallel to the slide rods 55,and which at one end is threaded through the casting 50 -and at itsother end is provided with a diametrally reduced smooth end-portion 66fitting for rotation in, and extending through, the crosscasting 56.Fixed, as by means of a diametral pin for indexing co-operation with thegraduations on the knob-skirt 36. In this connection, it

should be noted that the 0 graduation of the knob-skirt 36 and thereference mark 39 are so set in relation to the threads of the screw 33as to be in precise registration when the graduation line 21 of thecarriage-ear 24 and its asso- 61, upon the end-portion'of the screw 66,is a flanged or'skirted feed-wheel 68, in turn, provided with aprojecting handle 69 and having inscribed upon its peripheral face asuitable circumferential series of graduations or scale markings, all asbest seen in Figures 1 and 3.

` Secured to and upon the head-block 59 as by means of an attachmentbolt 10 threaded into the tapped drill hole 59, as best seen in Figure3, is a jig-plate 1| provided on its under face with a milled slot 12for snug-fitting engagement with the tongue 63. f

At its outer or free end, the jig-plate 1| is laterally extended, as at13, and is arcuately curved along its outer margin for substantiallyconforming to the shape or contour of the brake shoe B, the plate 1|centrally of its outer or arcuate margin being recessed or cut away inthe provision of a clearance space, as at 14.

Set into the upper face of, and spaced inwardly fromfthe outer arcuatemargin of, the jig-plate 1 is a pair of upstanding pins 15 positionedequidistantly on opposite sides of the longitudinal axis of thejig-frame 49 for engagement with the rear arcuate face of the brake shoeB.

In this connection, it should be noted that a jig-plate, such as theplate 1 I, should be provided for each different size of brake shoe, and'in each case the several dierent jig-plates 1I differ from each otheronly in that the pins are located at a distance from the vertical axisof the pintle 43 which is substantially equivalent to the radius of theinner face of the particular brake shoe which the selected jig-plate isdesigned to support.

Removably co-operable with the several jigplates 1|, is a somewhattriangular jig clamp 1B provided at its one or base end with a pair ofdepending prongs 11 for engagement with the upper face oi the brake shoeange f and at its other or' apex end with a depending lug 18 having alateral arm 19, in turn, equipped with 4a. thumbscrew 89 for engagementat its lower end with the bolt 19 or some other suitable portion of thejig-plate 1| for adjusting themain body of the clamp 16 to substantiallyparallel relation with the jig-plate 1|.

The clamp 16 is further provided with a. closedend slot 8| for looselyaccommodating a jig clamp attachment screw 82 preferably integrallyprovided adjacent its lower end with a diametrally enlarged abutmentcollar 83 for stop-engagement with the upper face of the jig-plate 1|and at its upper end with a spoke-handled clamp nut 84.

Coiled on the screw 82 intermediate the under face of the jig clamp 16and the upper face of the abutment collar 83, is a compression spring 85for normally urging the jig clamp 16 upwardly against the clamping nut84 for facilitating attachment and removal of the jig clamp 1B from anyselected one of the jig-plates 1I with which it is to be used during agiven grinding or abrading operation.

Adapted for rotatable disposition upon the upper bearing-forming endportion 48 of the pintle 43, as b'est shown in Figures 8 and 9, is ameasurement adapter including a hubbed disk 86 provided with anintermediate portion 81 contoured for tting snugly within an opening 88of a brake drum caliper 89 of the type fully disclosed and described inLetters PatentNo. 2,187,962, issued to me on January 23, 1940.

Also provided for detachable engagement as by means of bolts 99 to thecasting 59 when the jig frame 49 is removed from the pintle pin 43, is asplit collar or bearing hub 9| having a pair of laterally projectingsuitably tapped bosses 92 for receiving the attachment bolts 99 and apair of opposed clamping ears 93 drawn together by a conventional clampscrew 94.

Similarly mounted upon the jig frame cross head 59 by means of asuitable bolt 95 threaded into the tapped hole 69, is an L-shapedbracket 96 having a leg portion 91 offset, a; at 98, to provide aclearance recess 99 and at its lower end provided with a transverseshoulder |99 machined upon its outwardly presented face and having acentrally disposed lengthwise extending tongue |9| for snug-fittingengagement in the slot 94 of the jig frame head block 59. At its otherend, the bracket leg 91 is preferably integrally connected with alaterally extending arm |92 having an outwardly presented machined face|93 disposed in a plane parallel to the longitudinal axis of the jigframe 49 and provided with a lengthwise extending slidewayy |94, inturn, provided in its bottom wall with a closed-end slot for adjustablyaccommodating a self-contained motor-driven face wheel grinder |98 ofthe type substantially more fully described in my said Letters PatentNo. 2,187,962.

In use and operation, the jig frame 49 may be mounted, as described, onthe carriage 2| by inserting the lower bearing-portion 44 of the pintle43 through the journal 53 of the jig frame casting 59, and the pintle 43threaded into a selected tapped opening 39 of the carriage 2|corresponding to the diameter of the work, that is to say, in thepresent instance, the particular brake shoe being ground. Thus, if ashoe for a twelve inch brake drum is being ground, the pintle 43 willlbe threaded into the tapped drill hole or opening 39 marked 12, as bestseen in Figure 1.

The appropriate jig-plate 1| also designed for a twelve inch brake drumis bolted upon the jig frame head block 59, and a brake shoe B clampedthereon with its rearwardly presented arcuate face held tightly againstthe pins 15 by means of the jig clamp 16, care being observed to adjustthe jig clamp thumb screw 89 in such manner that, when the clamp nut 84is tightened, the web or body portion of the jig clamp 16 will besubstantially parallel to the jig plate 1|, as best seen in Figures 2and 3.

Thereupon, the feed wheel 68 of the jig frame 49 -is appropriatelyrotated to shift the jig frame rods 55 and the associated jig-plate 1|,together with the clamped brake shoe B, longitudinally `with respect tothe jig frame casting 59 for engaging the particular brake shoe B withthe abrading disk or surface I4 of the grinder wheel I3 when the jigframe 49 is oscillated upon the pintle 43. The entire jig frame 49 andits supported brake shoe is then manually oscillated in a horizontalplane around the pintle 43 as a bearing, and once the brake shoe B hasbeen fed toward, and comes into contact with, the abrading surface I4,the oscillations of the jig frame 49 will elect a truly concentricarcuate surface to be ground on the brake shoe B.

It is preferable that the feed increment after each cut should be small,so that the successive cuts will be relatively light. Obviously in suchcase, the rst few cuts which are ground o of the particular brake shoe Bwill ordinarily fail to grind a complete and continuous surface, byreason of eccentricities and irregularities in the surface which mustrst be removed by the initial grinding operations. After severalsuccessive cuts have been taken, however, a smooth continuous and trulyconcentric surface will be formed upon the brake shoe B.Y As soon as theground surface becomes continuous over the entire operating face of thebrake shoe B, the grinding operation may be continued or stopped,depending upon the thickness of the lining or block which has beenapplied to the brake shoe B. but it should be specifically noted that,irrespective oi' the number of successive cu taken,

only the thickness of the lining will change. 'Ihe curvature of theground surface will always remain identical, that is toV say, thesurface formed upon the particular brake shoe B will always be thesegment of 'a truly concentric cylinder having a radius exactly equal'tothe distance between the plane ofthe grinding surface I4 and the pintle43.

In many instances, after the braking surface has been satisfactorilyground, it becomes desirable to chamfer or bevel the outer transversemargins of the attached brake lining. To accomplish this result, theparticular brake shoe B is ground in the manner described, and, uponcompletion of such grinding operation, the clamp portion 26 of thecarriage 2| is loosened and the jig frame 49 shifted to, and held in,such position as to present thertransverse margin of the particularbrake lining toward the grinding wheel I3.

Thereupon, the handle 4| is swung in the direction of the arrow, Figure7, effecting through engagement with the grinding wheel I3 a chamferingof such transverse margin of the brake shoe lining. As soon as the brakeshoe lining has been suillciently beveled, the handle 4I is released andthe carriage 2| yieldingly returns to original position under influenceof the spring 33. Thereupon the operation may be repeated for theopposite transverse margin of the brake shoe lining.

In numerous cases, brake shoes and drums which must be ground are knownto be oversized or under-sized by a certain amount. If, for example, inthe particular automobile or truck which is being repaired, themanufacturer has designed the brake drum and shoe to be a twelve inchdrum which is 0.010 under-size, the carriage clamping portion 26 isloosened and the knob 35 of the carriage feed screw 33 turned to bringthe appropriate graduation opposite the index or reference mark 39, soas to swing the carriage 2| about the pivot screw 20, shifting thepintle 43 away from the grinding plane of the Wheel I3 by a sufficientdistance to compensate for the under-size measurement of such particularbrake shoes and drums.

Frequently the brake drums and shoes of a particular truck or automobilewill have been turned down and resurfaced to such an extent that theamount by which the drum is over-size is not known. It, therefore,becomes necessary to measure the brake drum by means of the brake drumcalipers 89, the latter being employed in the manner described in mysaid Letters Patent No. 2,187,962. The caliper is then fitted with thehubbed disk or adapter 86 and placed upon the upper bearing-forming endof the pintle 43. The carriage 2| is thereupon shifted inwardly oroutwardly by means of the knob 35, as described, until the calipers maybe swung around into bearing touching contact with the abrading surfaceI4 of the grinder wheel I3, as shown in Figures 8 and 9. Finally, thecarriage clamping bolt 26 is tightened down t0 hold the carriage 2| insuch adjusted position and the grinding operation carried out intheusual manner.

It often is desirable in brake repair work to grind a brake liningsurface on the Wheel. In such case, the jig frame 49 may be bodilyremoved from the carriage 2| and tted with the accessory bearing hub 9|,the grinder support bracket 9'I, and the portable grinder |06, as shownin Figures 10 and 1l, thus forming a portable grinder substantially ofthe type disclosed and described in my said Patent No. 2,187,962, whichmay be used in precisely the manner therein set forth.

lI may also provide a combination brake relining machine C including avertically disposed grinding cylinder |01 mounted von a single support I08 with suitable rivet upsetting and removing devices D, E, of the typesubstantially described in Letters Patent No. 2,109,327, issued to me onFebruary 22, 1938, and No. 1,949,070, issued to me on February 27, 1934,and having a flat steel adapter plate |09 suitably bored for attachmentby means of bolts ||0 to the machine support or base |08 of such acombination brake relining machine C. Swingably mounted upon the uppermachined face of the adapter plate |09 A by means of a pivot screw 20',is a carriage 2|',

identical in every respect to the carriage 2 I, for receiving a pintle43 and a jig frame 49. Welded or otherwise suitably secured upon theforwardly presented transverse margin of the adapter plate I 09 andpositioned in outwardly spaced relation to the adjacent margin of themachine bed |08, is a suitably bored and tapped depending flange I IIfor receiving the carriage feed screw 33. The adapter plate |09 issuitably drilled and tapped for receiving a carriage clamping screw 26for holding the carriage plate at the proper position of 0" adjustmentin reference to the grinding plane of the vertical grinding cylinder|01, so that the centers of the several tapped holes 30 will be properlypositioned, the carriage 2| and frame 49 functioning as described inabrading a particular brake shoe.

It will be noted that the slide rods 55 of the jig frame 49 are veryconveniently secured in adjusted positions by means of a suitable setscrew or the like |20 threaded in the frame or casting 50, as best seenin Figures 1 and 14.

The machine fulfills in every respect the objects stated, and it shouldbe understood that other changes and modifications in the form,construction, arrangement, and combination of the several parts of themachine may be made and substituted for those herein shown and describedWithout departing from the nature and principle of my invention.

Having thus described my invention, what I claim and desire to secure byLetters Patent is:

1. In a grinding machine, in combination, grinding means, a base, ajig-member pivoted on the base for oscillation, a pair of spacedparallel slide-bars extending lengthwise for movement through thejig-member, a block mounted on said rods for supporting a brake-shoe foroscillation with the jig-member relatively to the grinding means, andmeans for longitudinally shifting said bars for selectively locating theblock and its supported shoe with respect to the grinding means andjig-member.

2L. In a grinding machine, in combination, grinding means, a base, ajig-member pivoted on the base for oscillation, a pair of spacedparallel slide-bars extending lengthwise for movement through thejig-member, a block mounted on said rods for supporting a brake-shoe foroscillation with the jig-member relatively to the grinding means, across-bar xed to the slide-bars, and a threaded member having rotaryconnection with said cross-bar and threaded connection with thejig-member for longitudinally shifting the slide-bars for selectivelylocating the block and its supported shoe with respect to the grindingmeans and jig-member.

3. In a grinding machine, in combination, grinding means, a base, ajig-member pivoted on the base for oscillation, a pair of spacedparallel slide-bars disposed upon opposite sides of the pivot of, andextending lengthwise for movement through, the jig-member, a blockmounted on the forward end of said rods for supporting a brake-shoe foroscillation with the jig-member relatively to the grinding means, across-bar xed to and upon the rear end of the slide-bars, and a threadedmember disposed lengthwise intermediate and in parallel relation to saidbars and having rotary connection with said cross-bar and threadedconnection with the jig-member for longitudinally shifting theslide-bars for selectively locating the block and its supported shoewith respect to the grinding means and jigmember.

4. In a grinding machine, in combination, grinding means, a base, ajig-member pivoted on the base for oscillation, a pair of spacedparallel slide-bars extending lengthwise for movement through thejig-member, a block mounted on said rods for supporting a brake-shoe foroscillation with the jig member relatively to the grinding means, meansfor longitudinally shifting said bars for selectively locating the blockand its supported shoe with respect to the grinding means andjig-member, and means for indexing the longitudinal movement of the barsand their supported block with respect to the grinding means.

5. In a grinding machine, in combination, grinding means, a base, ajig-frame including a head-block pivoted on the base for oscillationrelatively to the grinding means, a jig-plate secured on the block forsupporting a brake-shoe, said plate being laterally extended andarcuately curved along its cuter margin for substantially conforming tothe contour of a supported brakeshoe, spaced pins upstanding from theplate equidistantly on opposite sides of the longitudinal axis of thejig-frame for engagement with the rear arcuate face of the supportedbrakeshoe, a triangular jig-clamp adapted for disposition over thejig-plate and the supported brakeshoe, said clamp being provided at itsbase end with a pair of depending prongs for engagement with the upperface of the supported brake-shoe and at its apex with a depending lughaving a lateral arm, means engaging said arm for adjustably disposingthe jig-clamp in substantially parallel relation with said plate, andmeans for securing the clamp to said plate in shoe engagement.

6. In a grinding machine, in combination, grinding means, a base, acarriage in the form of a at rectangular plate disposed over the base,said plate having an ear projecting from a corner thereof and at saideary being pivotally attached to the base, and a brake-shoe supportingjigframe pivoted for oscillation on the carriage with its pivot pointdisposed on a line at right angles to the grinding means for normallyconcentri cally engaging the supported shoe with the grinding means, thecarriage being arcwise adjustable with respect to the base for angularlyshifting the pivot point of the jig-frame from said line forcorrespondingly shifting the jigframe for abnormally eccentricallyengaging the supported shoe with the grinding means.

7. In a grinding machine, in combination, grinding means, a base, acarriage in the form of a plate disposed over, and for swingableadjustment pivotally attached to, the base, a brakeshoe supportingjig-frame pivoted for oscillation on the carriage, and means includingan arcuate pin-accommodating slot onthe carriage for securing thecarriage in selected swingable adjustment to the rbase for angularlyvarying the location of the pivot point of the jig-frame with respect tothe grinding means.

8. In a grinding machine, in combination, grinding means, a base, acarriage in the form of a plate disposed over, and for swingableadjustment pivotally attached to, the base, a brakeshoe supportingjig-frame pivoted for oscillation/ on the carriage, means for securingthe carriage in a selected swung position on the base for angularlyvarying the location of the pivot point of the jig-frame with respect tothe grinding means, and means `for indexing the selected swung positionof the carriage with respect to the base.

9. In a grinding machine, in combination, grinding means, a base, acarriage in the form of a plate disposed over, and for swingableadjustment pivotally attached to, the base, a brakeshoe supportingjig-frame pivoted for oscillation on the carriage, means for securingthe carriage in a selected swung position on the base for angularlyvarying the location of the pivot point of the jig-frame With respect tothe grinding means, and means including a threaded member havingengagement with the carriage and the base for indexing the swungposition of thc carriage with respect to the base.

10. In a grinding machine, in combination,

grinding means, a base, a carriage in the form of an L-shaped platecomprising longitudinally and transversely extending arms disposed over.and for swingable adjustment pivotally attached at the free end of itstransverse arm to, the base, the longitudinal arm of said plate beingprovided with a line of spaced apertures, a pivot-pin disposed in aselected aperture of said arm, and a brake-shoe supporting jig-frameengaged with said pivot for oscillation on the carriage relatively tothe grinding means and base.

11. In a grinding machine, in combination, grinding means, a base, acarriage in the form of an L-shaped plate comprising longitudinally andtransversely extending arms disposed over, and for swingable adjustmentpivotally attached at the free end of its transverse arm to, the base,the longitudinal arm of said plate being provided with a plurality ofseries of spaced apertures,a pivot pin disposed in a selected apertureof said arm, and a brake-shoe supporting jig-frame engaged with saidpivot for oscillation on the carriage relatively to the grinding meansand base.

12. In a grinding machine, in combination, grinding means, a base, acarriage in the form of an L-sha'ped plate comprising longitudinally andtransversely extending arms disposed over, and for swingable adjustmentpivotally attached at the free end of its transverse arm to, the base, abrake-shoe supporting jig-frame pivoted for oscillation on the carriage,and means including an arcuately pin-accommodating slotted earprojecting outwardly from the opposite end of the transverse arm of thecarriage for securing the carriage in selected swung'position on thebase for angularly varying the location of the pivot point of theJig-frame with respect to the grinding means.

HARRY B. BARRETT.

